The present invention relates to an internal-combustion engine provided with a recirculating system for exhaust gases and, in particular, to a internal-combustion engine of the diesel type for a vehicle, to which the following description refers without thereby implying any restriction.
It is known that internal-combustion engines comprise a plurality of cylinders and a cylinder head which, for each cylinder, has at least one intake duct for outside air and at least one exhaust duct which communicates with an exhaust manifold adapted to convey the exhaust gases from all the exhaust ducts associated with the cylinders.
Engines are known which are provided with systems for recirculating the exhaust gases so as to recirculate some of the gases from exhaust manifold to the intake ducts, in particular for the purpose of containing polluting emissions based on nitrogen oxides with in preset limits. These recirculation systems, which are commonly denoted by the acronym EGR (xe2x80x9cexhaust gas recirculationxe2x80x9d), comprise a control valve operated by suitable means for varying the flow rate of the exhaust gases bled from the exhaust manifold, and a recirculation pipe interposed between the exhaust manifold and a further manifold adapted to distribute said gases into the intake ducts.
In general, the EGR system further comprises a heat exchanger, normally of plate type, which is arranged in series with the recirculation pipe and which is adapted to lower the temperature of the recirculated gases so as to improve the efficiency of the system and the efficiency of the engine.
The known EGR systems of the type just described are expensive as a result of using a heat exchanger having characteristics which are compatible with the exhaust gases, and they have relatively long assembly times since they require a relatively large number of components to be attached and connected to one another, such as the heat exchanger and the various lengths of piping, it being necessary, however, to ensure satisfactory fluidtightness in the various couplings between the components themselves.
Moreover, the designing of the aforesaid components has to take into account the thermal distortion differing from one component to another, with the provision of expensive and delicate thermal compensation elements, for example bellows-type pipes.
Furthermore, the amount of space occupied by the heat exchanger can cause difficulties in the designing of the lay-out of the various units to be accommodated in the engine compartment, as well as in the operations of mounting/dismounting, periodical inspection and maintenance of the units themselves in the engine compartment.
The object of the present invention is to devise an internal-combustion engine, in particular for a vehicle, which makes it possible to solve the above-mentioned problems in a simple and economical manner.
An internal-combustion engine, in particular for a vehicle, is devised according to the present invention, comprising a plurality of cylinders; a cylinder head defining, for each cylinder, at least one exhaust duct for the exhaust gases and at least one intake duct; an exhaust manifold communicating with said exhaust ducts; and a system for recirculating exhaust gas from said exhaust manifold to said intake ducts, and comprising a distribution manifold for distributing the recirculated exhaust gases to said intake ducts, and a recirculation duct extending between said exhaust and distribution manifolds; characterised in that at least one portion of said recirculation duct is provided directly in said cylinder head; said cylinder head comprising heat exchange means for cooling said recirculated exhaust gases.